Conventionally, the amount of traffic traveling through fiber optic communication networks has been steadily changing and increasing explosively as is represented by data centers. Moreover, the number of network-node equipments accommodated on a fiber optic communication network and the types of data are becoming various, and it is becoming necessary to dynamically change the network topology, connection configuration, or even traffic capacity. For instance, in the current local public network described in “Proposal for local electronic government synergistic IDC operation for local electronic government implementation” (Chikafumi Shimura, Local management newsletter, vol. 34, June 2001, Nomura Research Institute), there has been a call for: interconnection of municipal networks having different network topologies; installation of additional network-nodes or network-node removal; network topology reconfiguration following organizational integration or organizational expansion; and dynamic implementation of wavelength path reconfiguration in order to bypass failures. Also, there has been a strong call for integration of networks having different network topologies while maintaining their securities, and for superposing and operating networks having different signal formats and operation policies simply and inexpensively. Accordingly a fiber optic communication system has been expected in which connections with any network-node can be selectively established and logical network topologies can be arbitrarily reconfigured, by changing the wavelength of optical signals used for the connection between network nodes, by a wavelength tunable light source unit and a wavelength tunable optical receiver unit installed on network-node equipments in a fiber optic communication network that is physically connected to a uniform-loss and cyclic-frequency (ULCF) arrayed wavelength grating (AWG) in a star-shape via an optical wave guide such as an optical fiber (see also: K. Kato et al, “32×32 full-mesh (1024 path) wavelength-routing WDM network based on uniform-loss cyclic-frequency arrayed-waveguide grating”, Electronics Letters, vol. 36, 1294-1296, 2000).
On the other hand, in investigations so far, networks are being advanced in which the connection configuration of optical wave guided paths such as optical fibers, which are transmission paths, physically has a ring topology (for example, Japanese Unexamined Patent Application, First Publication No. 2001-285323, Japanese Unexamined Patent Application, First Publication No. Hei 7-202845, and Japanese Unexamined Patent Application, First Publication No. 2001-184408).
For example, the network-node equipment disclosed in Japanese Unexamined Patent Application, First Publication Hei 7-202845 is constructed as shown in FIG. 4-37. An optical splitter (4-1) is one which splits an input optical signal into two regardless of its wavelength. An optical signal having eight wavelengths which is transmitted through the optical fiber is input thereto, and signals are output to an optical filter 4-2, a fixed-wavelength receiver unit A (4-4), and a fixed-wavelength receiver unit B (4-11).
The optical filter 4-2 has a function of intercepting from among the optical signals of eight wavelengths outputted from the optical splitter 4-1, two wavelengths, λs (short wavelength) and λe (long wavelength) that the network terminal transmits and receives, and transmitting the other wavelengths.
An optical combiner 4-3 combines the optical signals of six wavelengths transmitted from the optical filter 4-2 and optical signals of two wavelengths (λs, λe) outputted from a wavelength tunable transponder unit A (4-7) and a wavelength tunable transponder unit B14, and transmits them to optical fibers (not shown). The optical signals transmitted are inputted to the optical splitter 1 of the neighboring network-node equipment via an optical fiber (not shown in the diagram).
The fixed-wavelength receiver unit A (4-4) comprises a fixed-wavelength optical filter and a photodetector, and has a function of receiving only the optical signal of wavelength λs from among the optical signals of two wavelengths (λs, λe) outputted from the optical splitter 4-1, and converting the signal into an electrical signal. Similarly, the fixed-wavelength receiver unit B (4-11) receives only the optical signal of wavelength λe, and converts it into an electrical signal.
Selectors A and B (4-5 and 4-12) respectively reference received destination information assigned to the received data, and output the received data to a data processing module if the received data is addressed to the own network-node equipment. Also, if the received data is not addressed to the own network-node equipment and is to be relayed, the received data is outputted to a predetermined dual port memory of memory units A and B according to the received destination information.
Memory units A and B (4-6 and 4-13) have two dual port memories for data that specifies the wavelength of launched optical signal for every wavelength of launched optical signal, and one dual port memory for the data that does not specify the wavelength of launched optical signal.
The wavelength tunable transponder units A and B (4-7 and 4-14) have a function to convert the transmitted data into an optical signal and transmit it with two respective wavelengths: wavelength λs and wavelength λe. The wavelength tunable transponder unit A (4-7) is paired with the fixed-wavelength receiver unit A, and the wavelength tunable transponder unit 4-14 is paired with the fixed-wavelength receiver unit B (4-11).
A data processing module 4-8 of the network-node equipment performs the requested process for the data transmitted from other network-node equipment while performing processes such as assigning received destination information for the data that is to be transmitted from the own network-node equipment to another network-node equipment, and outputs the data to the memory unit A (4-6) or the memory unit B (4-13).
An end of transmission detection unit 4-9 detects the transmission end of the data stored in each of the dual port memories of the memory unit A (4-6) and the memory unit B (4-13), and outputs a wavelength switch signal to a wavelength controlling unit 4-10. The wavelength controlling unit 4-10 controls the oscillating wavelengths used for the wavelength tunable transponder units A and B to be λs and λe, by regulating the injection current of a tunable laser diode (hereunder referred to as TLD), which is described later.
However, when designing a network or changing a network configuration, although there are methods for configuring a plurality of different virtual LANs (VLAN) as different respective logical network topologies in the reconfiguration of logical network topologies, in the installation of a new network-node equipment or removal of network-node equipment, and in the reconfiguration of a logical network topology in order to circumvent failure, there is complexity in each of the various kinds of settings, and a few months to six months is required for the construction. Also these operations have required a lot of work and there has been the problem of the risk of network collapse and so forth caused by human error. Moreover, although it has been possible, by using technology such as traffic engineering (TE) that is capable of selecting routes. according to the amount of traffic, to reconfigure the logical network-topology according to the load on the network, cases in which the amount of traffic exceeds expected traffic are conceivable, such as distributing live concert video images or providing information in a time of disaster, and the complexity of network setting operations and the problems in stable network operation still remain for the present technology. Moreover cases in which it has been necessary to review and reconfigure the physical network topology that have been determined according to the connection configuration of optical fibers have not been few.
Also, the same is true even with reconfiguration of logical network topology using wavelength path by wavelength division multiplexing (WDM) technology, and this operation also requires work, and dynamic and quick reconfiguration of a logical network topology has been comparatively difficult.
When automatizing in order to treat these problems, although a collective management method by central-management-equipment or a method of assigning a setting to each individual equipment are common, in the former method, since multiple control information is required to control the wavelength tunable light source and wavelength tunable filter that are provided for the network-node equipments, then when performing network topology reconfiguration, the number of network-node equipments and the load on the central-management-equipment increase, and fast topology reconfiguration has been made difficult. Moreover, in the latter method, since settings for the wavelength tunable light source and the wavelength tunable filter need to be assigned separately to different network-node equipments, the load on the network administrator has increased in initial network configuration or in network reconfiguration when changing the network topology.
Furthermore, in the network system described in Japanese Unexamined Patent Application, First Publication No Hei 7-202845 mentioned above, in which a management method is explained, a network-node equipment autonomously performs controls related to search and determination of the wavelength of optical signals used for connection with other network-node equipments. However the two wavelengths to be used are not regulated to be just two successive adjacent wavelengths, and when the case of connections with many network-node equipments using more than two wavelengths is considered, there is concern of an increase in processing time required for the data processing module in the network-node equipment shown in FIG. 4-34.
However, in actual fiber optic communication systems, topology reconfiguration needs to be performed promptly according to changes in traffic pattern or efficient network usage, and in terms of stable network operation it is preferable not to require a long time from the start of the topology reconfiguration to its completion, and it has been desirable that high-speed topology reconfiguration be made possible.
In view of the problems mentioned above, it is an object of the present invention to provide a logical topology reconfigurable optical network system, a central-management-equipment, and a wavelength tunable light source unit thereof, and a network-node equipment into which is installed a wavelength tunable optical receiver unit and a computer program thereof, which are applicable to a geographically-distributed iDC (Internet Data Center) implemented for a local administrative network and to an IX (Internet exchange) network, and in which, installation and utilization of the logical topology reconfigurable optical network system, which is realized with a wavelength path routing function of an arrayed waveguide grating (AWG) and wavelength tunable light sources mounted on network-node equipments that are physically connected to the AWG in a star shape via optical waveguides such as optical fibers, can be achieved.
Moreover it is an object to provide an actual fiber optic communication system in which clock time synchronization of all network-node equipments can be performed by a central-management-equipment, and wavelength information for forwarding data signals and wavelength information for receiving data signals required for logical network topology reconfiguration, are transmitted along with trigger time information for logical topology reconfiguration from the central-management-equipment to network-node equipments, and in which network-node equipments can autonomously change wavelengths of launched optical signals and receiving optical signals at high speed when the reconfiguring time of the logical network topology is reached.